There has been a long felt need in the floor covering industry for a floor covering which can be applied directly to a concrete slab subject to moisture penetration. Some of the problems encountered with early materials such as degradation by moisture and lack of dimensional stability have been overcome by the use of sheet vinyl covering material having a substrate or backing layer of dimensionally stable materials such as asbestos felt or glass mat. The permeable nature of such substrates has however allowed moisture from the floor to penetrate through the substrate of the flooring material to intermediate layers thereof which frequently include an intermediate layer of foamed resinous material. Since such sheet vinyl materials usually have a plastic wear layer over the foamed layer, moisture migrating into the foamed layer from the concrete floor has tended to carry dissolved salts leached from the concrete into the foamed layer, because the wear layer is typically non-porous, such salts have tended to accumulate immediately beneath the wear layer thereby resulting in discoloration of printed patterns on the foamed layer and growth of unsightly fungi, etc.
One solution to these problems is suggested in U.S. Pat. No. 4,128,688, the disclosure of which is incorporated herein by reference. This patent describes a floor covering material of the general type described above in which a barrier layer overlies the moisture permeable backing layer with the barrier layer being dimensionally stable under varying moisture conditions and substantially impervious to moisture penetration. Polyvinyl chloride (PVC) resin together with plasticizer, heat and light stabilizer and fungicide is disclosed as being suitable for such a barrier layer. Barrier layers of the above mentioned patent are preferrably applied over a latex seal coated asbestos felt backing with the barrier layer being applied preferrably in thicknesses of approximately 0.5 millimeter.